1. Field of the Invention
The present invention relates to osmotic delivery systems for delivering beneficial agents, and more particularly, to an osmotic delivery system having a piston with a recess for receiving an osmotic agent.
2. Description of the Related Art
Controlled delivery of beneficial agents, such as drugs, in the medical and veterinary fields, has been accomplished by a variety of methods. One method for controlled prolonged delivery of beneficial agents involves the use of osmotic delivery systems. These devices can be implanted to release beneficial agents in a controlled manner over a preselected time or administration period. In general, osmotic delivery systems operate by imbibing liquid from the outside environment and releasing corresponding amounts of the beneficial agent.
A known osmotic delivery system, commonly referred to as an xe2x80x9cosmotic pump,xe2x80x9d generally includes some type of capsule or enclosure having a semipermeable portion that may selectively pass water into an interior of the capsule that contains a water-attracting osmotic agent. In such a known osmotic delivery system, the walls of the capsule are substantially impermeable to items within and outside the capsule, and a plug acts as the semipermeable portion. The difference in osmolarity between the water-attracting agent and the exterior of the capsule causes water to pass through the semipermeable portion of the capsule, which in turn causes the beneficial agent to be delivered from the capsule through the delivery port. The water-attracting agent may be the beneficial agent delivered to the patient. However, in most cases, a separate osmotic agent is used specifically for its ability to draw water into the capsule.
In some instances, a piston is required to separate the beneficial agent from the osmotic agent to prevent the osmotic agent from mixing with or contaminating the beneficial agent. The structure of the capsule is such that the capsule does not expand when the osmotic agent takes in water and expands. As the osmotic agent expands, pressure causes the piston to move and the beneficial agent to be discharged through the delivery orifice at the same rate as the liquid, which is typically water, enters the osmotic agent by osmosis. Osmotic delivery systems may be designed to deliver a beneficial agent at a controlled constant rate, a varying rate, or in a pulsatile manner.
In those osmotic delivery systems that require the use of a piston to separate the beneficial agent and the osmotic agent, the piston necessarily occupies space in the capsule. Hence, if the piston is needed to separate the beneficial agent and the osmotic agent, and the size of the capsule is not changed, the amount of beneficial agent or osmotic agent that can be held within the capsule decreases as compared to another osmotic delivery system having the same size capsule that does not include a piston. Decreasing the amount of beneficial agent within the capsule detrimentally decreases the net amount of beneficial agent that can be delivered over a sustained period of time. Decreasing the amount of osmotic agent within the capsule detrimentally decreases the sustained period of time through which continuous delivery of the beneficial agent can be obtained.
But if the specific application requires a specific amount of beneficial agent or osmotic agent that cannot be varied and a piston must be used to separate the beneficial agent from the osmotic agent, the size of the capsule must be increased to accommodate for the extra space occupied by the piston such that the amount of osmotic agent or beneficial agent in the capsule does not vary. While simply increasing the size or volume of the capsule to accommodate for the extra volume occupied by the piston may appear to be a simple solution, because many osmotic delivery systems are destined for implantation in humans or animals, it is especially desirable to decrease the size of the osmotic delivery system as much as possible, while still allowing the osmotic delivery system to deliver the beneficial agent over a prolonged period of time. Additionally, simply increasing the size of the capsule for those applications requiring a piston that separates the beneficial agent from the osmotic agent is inexpedient as it is desirable to use one capsule for multiple osmotic delivery system applications. Moreover, it has been particularly problematic to increase the amount of time over which steady state release of the beneficial agent may be obtained with current osmotic delivery systems incorporating conventional pistons, without increasing the size of the capsule to hold more beneficial agent or osmotic agent. These problems associated with current osmotic delivery systems having known pistons have created a need for a solution.
Generally speaking, the present invention provides an osmotic delivery system that strives to efficiently utilize the space within the enclosure of the osmotic delivery system.
The present invention strives to address the disadvantages of known osmotic delivery systems by providing an osmotic delivery system having a capsule. The capsule has an interior for holding a beneficial agent. The interior has an interior surface. An osmotic agent is located in the interior of the capsule. A semipermeable body is in liquid communication with the capsule and permits liquid to permeate through the semipermeable body to the osmotic agent. A piston is located within the interior of the liquid impermeable capsule. The piston is movable with respect to the interior surface of the capsule, and defines a movable seal with the interior surface of the capsule. The movable seal defined by the piston separates the osmotic agent from the beneficial agent. The piston has a recess that receives at least a portion of the osmotic agent. The osmotic agent is located between the piston and the semipermeable body. The osmotic agent imbibes liquid from a surrounding environment through the semipermeable body to cause the piston to move and in turn cause delivery of the beneficial agent from the capsule.
In accordance with another aspect of the present invention an osmotic delivery system includes a piston having a recess. An osmotic agent is located within the recess. An enclosure has an interior that holds the piston and the osmotic agent. The piston is movable with respect to the enclosure. The enclosure has a semipermeable body in liquid communication with the osmotic agent that permits liquid to permeate through the semipermeable body to the osmotic agent. The osmotic agent imbibes liquid from a surrounding environment and causes the piston to move.
According to another aspect of the present invention, an osmotic delivery system includes a capsule having a tubular interior. A semipermeable body is located at least partially within the tubular interior. A piston is located within the tubular interior. The piston has a recess. The piston defines a seal with an interior surface of the tubular interior. The piston is movable with respect to the interior surface of the tubular interior and with respect to the semipermeable body. An osmotic agent is located at least partially in the recess and the tubular interior. A beneficial agent is located within the tubular interior. The piston separates the beneficial agent from the osmotic agent. The semipermeable body is located on the same side of the liquid impermeable piston as the osmotic agent.
Other objects, advantages and features associated with the present invention will become readily apparent to those skilled in the art from the following detailed description. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modification in various obvious aspects, all without departing from the invention. Accordingly, the drawings and the description are to be regarded as illustrative in nature, and not limitative.